Ensure visualization uses binning in provided histograms

[sebastien-rettie]

It seems that in the case where no binning is provided in the config but histograms with a given binning are passed to cabinetry, some of the visualization tools (e.g. cabinetry.visualize.data_mc) don't pick up this binning and default to uniform bins instead. Attached are example plots using the same config, but the customBins file explicitly specifies the bins in the config file, whereas the default file does not pick the binning up from the input histograms.

@alexander-held suggested a fix for this could be something like a corresponding optional metadata file that is automatically filled

customBins.pdf
default.pdf